Optical security element

ABSTRACT

The invention concerns an optical security element having a substrate layer, in which a first microstructure for producing a first optically perceptible effect is shaped region-wise in a surface region. The surface region is divided into microscopically fine pattern regions and a background region. The first microstructure is shaped in the pattern regions but not in the background region. The microscopically fine pattern regions in the surface region are arranged in the form of a moire pattern into which a concealed item of information which can be evaluated by means of an associated verification element is encoded as a security feature. The microscopically fine pattern regions are further substructured in accordance with a substructuring function which describes a microscopic substructuring, serving as a further security feature, of the moiré pattern.

The invention concerns an optical security element having a substratelayer, in which a first microstructure for producing a first opticallyperceptible effect is shaped region-wise into the substrate layer in asurface region of the substrate layer.

U.S. Pat. No. 6,351,537 B1 describes the use of a security element whichimplements a hologram and a concealed image on a common carriersubstrate. The hologram is a hologram which is visible in daylight andwhich is generated by an optical-diffraction structure shaped into aphotopolymer film and is visible without the use of a monochromatic,coherent light source (laser). The concealed image is preferablyarranged on the substrate in the proximity of the hologram. Theconcealed image is rendered visible by means of a decoding device.Digital copiers or scanners are used as the decoding device. Thatpublication also describes using a decoding device in the form of atransparent carrier on which a line grating is printed, with a linespacing corresponding to the desired scanning frequency.

The concealed image is produced from a starting image by a procedurewhereby firstly the frequency components of the starting image which aregreater than half the scanning frequency of the decoding device areremoved and the remaining frequency components are then mirrored at thefrequency axis which corresponds to half the scanning frequency.

In that way the substrate provides a first security feature, namely thehologram, and a second security feature, namely the concealed image,whereby the number of security features and thus the level of safeguardagainst forgery is increased.

U.S. Pat. No. 5,999,380 describes a holographic process for enhancingthe level of safeguard against forgery, wherein a concealed image isshaped in a hologram, which image can be perceived only by means of aspecial evaluation device. It is only when the evaluation device ismoved over the hologram that then the concealed image can be visuallydetected by the human observer.

In that respect, a hologram of that kind with a concealed image isproduced in an encoding process which is based on the one hand on abackground image and on the other hand the image to be concealed in thehologram. The background image comprises a larger number of parallelblack stripes. Now, in the encoding process, those parts of the patternto be concealed, which are over the black stripes of the backgroundimage, are converted into white and those parts of the image to beconcealed, which lie over the white part of the background image,.areleft black. In order to make the pattern which is concealed in the imageformed in that way still less perceptible for the naked eye of a viewer,the resulting image is further superimposed with an optical noisepattern.

The object of the invention is now that of further improving thesafeguard against forgery of optical security elements.

That object is attained by an optical security element in which a firstmicrostructure for producing a first optically perceptible effect isshaped region-wise into the substrate layer in a surface region of asubstrate layer, in which the surface region is divided intomicroscopically fine pattern regions and a background region and thefirst microstructure is shaped in the pattern regions but not in thebackground region, in which the microscopically fine pattern regions inthe surface region are arranged in the form of a moiré pattern intowhich a concealed item of information which can be evaluated by means ofan associated verification element is encoded as a security feature, andin which microscopically fine pattern regions are further substructuredin accordance with a substructuring function which describes amicroscopic substructuring, serving as a further security feature, ofthe moiré pattern.

In that respect a moiré pattern is a pattern which is formed fromrepeating structures and which upon superimposition with or viewingthrough a further pattern formed by repeating structures exhibits a newpattern which is concealed in the moiré pattern.

The superimposition of a moiré pattern with a decoding device providesthat the pattern concealed in the moiré pattern becomes visible due tothe moiré effect. The classic moiré effect arises out of the interactionbetween mutually superposed dark and light structures. It results fromthe geometrical distribution of dark and light regions in the mutuallysuperposed regions, wherein regions in which dark elements occur oneupon the other appear lighter than regions in which the dark elements ofthe mutually superposed regions are in mutually juxtaposed relationship.

The invention provides a security element which can be imitated onlywith very great difficulty by the interengagement of various securityfeatures. The substructuring of microscopic fine pattern regions of amicrostructure, which are arranged in the form of a moiré pattern,provides that additional items of information are encoded in the surfaceregion, which cannot be perceived either by the naked eye or by theverification element associated with the moiré pattern. The specificconfiguration of the structure can however be perceived with amagnifying glass or a microscope and serve as an additional securityfeature or for identification purposes. As the substructuring also hasan effect on the average surface coverage within the pattern regions ofthe moiré pattern, implementing changes in the substructuring also hasan action on the optical effects which become visible when checking thesurface region by means of a verification element associated with themoiré pattern. Thus for example alterations of that kind becomeperceptible by virtue of the occurrence of non-homogeneous regions(viewing with/without verification element) or due to a variation in theoptical effects which occur upon displacement or rotation of theverification element. The optical effects produced by thesubstructuring, the arrangement of the pattern regions and themicrostructure thus engage into each other and are in superposedrelationship, whereby imitation is made more difficult and forgeries areeasy to perceive.

In addition the optical effects generated by a security elementaccording to the invention cannot be imitated by means of a moiré imagecontained in a hologram. Imitation by means of conventional holographictechniques, as is possible for example in the mere implementation of aconcealed image in a hologram, is accordingly not possible. That furtherenhances the level of safeguard against forgery.

Advantageous developments of the invention are characterised in theappendant claims.

It is desirable to use a diffraction grating, a diffraction structurefor producing a first hologram or a matt structure as the firstmicrostructure. It has proven to be advantageous for a reflectingsurface, a transparent surface (micro-metallisation), a seconddiffraction grating which differs from the first diffraction grating, adiffraction structure for producing a second hologram or a second mattstructure which is different from the first matt structure, to be shapedin the background region.

The first and second diffraction gratings can in that case differ forexample in respect of azimuth angle, grating frequency or profile shape.

The term matt structures is used to denote structures having scatteringproperties. Those scattering properties can be produced by amicrostructure with a stochastic surface profile or by a diffractionstructure which has such properties. Diffraction structures of that kindcan also be produced holographically. The first and second mattstructures can involve isotropic or anisotropic matt structures.Isotropic matt structures have a symmetrical scatter cone whereasanisotropic matt structures exhibit an asymmetrical scatter behaviourand have for example a preferred scatter direction. In that respect thefirst and the second matt structures differ for example in the spreadangle of the scatter cone and/or in the preferred scatter direction.

It will be appreciated that it is also possible for the backgroundregion to have different microstructures.

The fact that a microstructure which is different from themicrostructure of the pattern region is shaped in the background regionmeans that further optical superimposition effects occur, whereby thelevel of safeguard against forgery of the optical security element isfurther improved.

In addition it is also possible to use micro-metallisation as a furthervariant for substructuring. The contrast is achieved by the differencebetween the reflecting layer and the transparent region. In that casethe pattern region can also be in the form of a mirror. In addition themicro-metallisation can be combined with a semitransparent HRI layer inthe background region. In addition the same optical-diffractionstructure can be present both in the pattern region and also in thebackground region, in which case the contrast is achieved by thedifferent reflection capability.

It is advantageous for the moiré pattern to comprise a line gratingcomprising a plurality of lines with a line spacing in the range of 40to 200 μm. That line grating is phase-displaced in region-wise manner toproduce the concealed information. In that case the phase displacementis preferably half a line grating period. Besides a linear line gratingit is also possible for the lines of the line grating to have curvedregions and for example to be arranged in a wave-shaped or circularconfiguration. Then, for decoding the concealed information, acorresponding verification element is required, which also has a linegrating which is of such a shape. In that way it is possible for thedecoding of the concealed information to be effected only by means of aquite specific, individual verification element, which further enhancesthe level of safeguard against forgery of the optical security element.There is also the possibility of the moire pattern being made up of twoline gratings which are rotated relative to each other through 90degrees. That affords the advantageous effect that not just one but twodifferent concealed items of information can be encoded in the moirépattern. Those items of information can be evaluated in succession byrotation of the verification element. That also enhances the level ofsafeguard against forgery of the optical security element.

The average surface coverage of the moiré pattern in relation to theresolution capacity of the human eye and the average surface coverage ofthe substructuring described by the substructuring function in relationto the resolution capacity of the human eye is preferably constant. Inthat way it is not possible for the human observer to recognise thepresence of further security features without auxiliary means.

Advantageous effects can be achieved if the average surface coverage ofthe moiré pattern in relation to the resolution capacity of the humaneye is constant, but the surface coverage of the pattern regions isvaried by partially different substructuring. In that way it is possibleto generate patterns which are optically perceptible to the human eye,in the surface region, by the substructuring, and that further enhancesthe safeguard against forgery.

The substructuring function preferably describes a continuoussubstructuring pattern. It is however also possible that thesubstructuring function describes a non-continuous substructuringpattern.

It is desirable for the substructuring function to describe asubstructuring pattern which is made up of a plurality of similarindividual elements. Further advantages can be achieved by virtue of thefact that the spacings of the individual elements or the orientationthereof are varied for encoding further items of information in thesubstructuring. Those additional items of information can be used as afurther security feature or for data storage. It is particularlyadvantageous if—as already stated above—in that case the average surfacecoverage, which can be resolved by the human eye, of the substructuringpattern remains constant.

Further preferred possible ways of introducing additional items ofinformation and security features by the substructuring provide that thesubstructuring function describes a microtext or nanotext orsuperimposes a two-dimensional grating. Preferred letter heights in themicrotext or nanotext in that case are in the range of 50 to 80 μm.Instead of a microtext or nanotext or in combination with such a textthe substructuring function can also describe nano-images which forexample are formed from pixels of a size of 1 μm×1 μm. Such a nano-imagecan also involve a corporate logo. Preferably nano-images of that kindare in a range of sizes of 20 μm to 100 μm.

Further advantageous effects can be achieved by the pattern regionsbeing substructured with an asymmetrical surface profile. By virtuethereof the substructuring has an effect in particular on the opticaleffects which are visible to the viewer upon displacement of theverification element. It is particularly advantageous here for only thecentroids of the pattern regions to be displaced in phase relative toeach other in region-wise manner to produce the items of concealedinformation, that is to say for the centroids and not the outlines ofthe pattern regions to be arranged in accordance with the moiré pattern.The pure line grating is resolved in that way so that even upon correctorientation of the verification element, there exist positions of theverification element, in which partial regions of non-phase-displacedand phase-displaced pattern regions are superimposed in respect of theiroptical effect.

The invention is described by way of example hereinafter by means of anumber of embodiments with reference to the accompanying drawings inwhich:

FIG. 1 shows a view in section of an optical security element accordingto the invention,

FIG. 2 shows a diagrammatic view of a surface region of the opticalsecurity element of FIG. 1,

FIGS. 3 a to 3 d show diagrammatic views of possible substructuringpatterns for an optical security element according to the invention,

FIG. 4 shows a diagrammatic view of a surface region of an opticalsecurity element according to the invention for a further embodiment ofthe invention,

FIGS. 5 a and 5 b show diagrammatic views of portions of surface regionsof optical security elements according to the invention for furtherembodiments of the invention,

FIGS. 6 a to 6 c show views of portions of surface regions of opticalsecurity elements according to the invention for further embodiments ofthe invention, and

FIG. 7 shows a diagrammatic view of a plurality of partial regions of anoptical security element according to the invention for a furtherembodiment of the invention.

FIG. 1 shows a stamping film 1 which comprises a carrier film 11 and atransfer layer portion 12 serving as an optical security element. Thetransfer layer portion 12 has a release and/or protective lacquer layer13, a replication layer 14, a reflection layer 15 and an adhesive layer16.

The carrier layer 21 comprises for example a polyester film of athickness of 12 μm to 50 μm. The release and/or protective lacquer layer13 is applied to that carrier film, in a thickness of 0.3 to 1.2 μm. Thereplication layer 14 is now applied to the release and/or protectivelacquer layer. The replication layer 14 is preferably a transparentthermoplastic material which is applied for example by means of aprinting process over the full area to the film body formed by thecarrier film 11 and the protective lacquer and/or release layer 14. Theapplication operation can be effected for example with a line gratingintaglio printing cylinder with an application weight of 2.2 g/mm afterdrying, the drying operation being effected in a drying passage at atemperature of 100 to 120° C. A microscopic surface structure is nowreplicated into the replication layer by means of a stamping tool inregions 17. For example in that way the microscopic surface structure isembossed at approximately 130° C. with a die comprising nickel.

It is however possible for the replication operation to be carried outby means of a UV replication process, wherein a UV replication lacqueris applied to the film body formed by the carrier film 11 and therelease and/or protective lacquer layer 13 and then partially irradiatedwith UV light for replication of the microstructure.

After replication of the microstructure in the replication layer 14 thereplication lacquer hardens by cross-linking or in some other fashion.

It is also possible for the microstructure to be shaped in the layer 14by means of holographic methods. For that purpose, in the holographicexposure operation, the background region is covered with a suitablemask or the microstructure is removed in the background region after theexposure operation.

A thin reflection layer 15 is now applied to the replication layer 14.The reflection layer 15 preferably involves a thin, vapour-depositedmetal layer or an HRI layer (HRI=‘High Reflection Index’). For exampleTiO₂, ZnS or Nb₂O₅ can be used as materials for an HRI layer. Thematerial for the metal layer can essentially be chromium, aluminium,copper, iron, nickel, silver, gold or an alloy of those materials. Inaddition instead of such a metallic or dielectric reflection layer, itis possible to use a thin film layer sequence with a plurality ofdielectric or dielectric and metallic layers.

The adhesive layer 16 is now applied to the film body formed in thatway, the adhesive layer comprising for example a thermally activatableadhesive.

For applying the optical security element to a security document or someother article to be safeguarded, the stamping film 1 is applied with thetransfer layer portion 12 leading to the security document or thearticle to be safeguarded and is then pressed under the effect of heatagainst the security document or the article to be safeguarded. In thatoperation the transfer layer portion is joined by way of the adhesivelayer 16 to the corresponding surface of the security document or thearticle to be safeguarded. In addition, as a consequence of thedevelopment of heat, the transfer layer portion 12 is detached from thecarrier film 11 which is now pulled off the transfer layer portion 12and removed. An optical security element according to the inventionwhich comprises the transfer layer portion 12 or parts of the transferlayer portion 12 is now applied to the security document or the articleto be safeguarded.

It will be appreciated that it is also possible for an optical securityelement according to the invention to be part of a transfer orlaminating film or to be formed by a stamping film, a sticker film, atransfer film or a laminating film. In addition it is also possible foran optical security element according to the invention to have furtherlayers besides the layers 13, 14, 15 and 26 shown in FIG. 1. Suchfurther layers can be for example (coloured) decorative layers or layersof a thin film layer system which produces colour shifts in dependenceon the angle of view, by means of interference.

In addition it is also possible for the reflection layer 15 to be onlypartially implemented or to be entirely dispensed with, so that theoptical security element acts as a transparent and not as a reflectivesecurity element. It would also be possible to dispense with theadhesive layer 16.

As already explained above, the microstructure is only replicated inregion-wise manner in the replication layer 14 so that in thereplication layer 14 there are regions 17 in which the microstructure isreplicated and regions 18 in which the microstructure is not replicatedinto the surface of the replication layer 14. FIG. 2 now shows a surfaceregion of the optical security element formed by the transfer layerportion 12, clearly showing the regions in which replication of themicrostructure in the surface of the replication layer 14 is effected.

FIG. 2 shows a surface region 2 which is divided into a backgroundregion 20 and a plurality of pattern regions 21 to 40. As shown in FIG.2 the pattern regions 21 to 39 are each substructured in accordance witha respective substructuring function, wherein the substructuringfunction describes a substructuring of the respective pattern region inthe form of a meander-shaped pattern. The pattern regions 22, 24 and 26are spaced from the pattern region 21 preferably at 40 to 300 μm. Such aspacing provides that on the one hand the optical effects produced bythe microstructures disposed in the pattern regions 21, 22, 24 and 26mingle in the human eye and are not individually resolved, and on theother hand sufficiently large individual surfaces are available for therespective shaped microstructure. The pattern regions 22, 24, 26, 27,29, 31, 32, 34, 36, 37 and 39 are then also correspondingly spaced fromeach other.

As shown in FIG. 2 in a V-shaped partial region 3 of the surface region2, the pattern regions 23, 28, 35, 38, 40, 35, 30 and 24 are arranged inphase-displaced relationship with respect to the pattern regions 21, 22,26, 27, 29, 31, 32, 34, 36, 37 and 39 surrounding them.

Accordingly the pattern regions 21 to 40 form a line grating which issubstructured by means of the above-described substructuring function,with a plurality of uniformly spaced substructured lines, with the linegrating being phase-displaced in the partial region 3 to produce theconcealed information.

A first microstructure is now shaped in the pattern regions 21 to 40.That microstructure preferably involves a diffraction structure of a 3Dor 2D/3D hologram.

It is further possible for the microstructure to be formed by adiffraction grating with a spatial frequency of more than 300 lines/mm.Preferred spatial frequencies of such a diffraction grating are in therange of 600 to 1800 lines/mm. In addition it can also be advantageousto use a diffraction grating with a very high spatial frequency which isless than the wavelength of the light. It is also possible to usezero-order diffraction gratings or asymmetrical diffraction gratings. Inthat case the grating parameters of the diffraction grating can beconstant in the pattern regions 21 to 40, but they can also be varied inorder thus for example to produce a kinegram® effect or other opticaleffects which generate an optical impression which is dependent on theviewing angle.

It is further possible for the microstructure to be a matt structurewhich is shaped in the pattern regions 21 to 40.

It is also possible to provide transparent regions by means of partialmetallisation in the pattern regions 21 to 40 whereas a diffractivestructure is provided in the background region 20.

No microstructure is shaped into the replication layer 14 in thebackground region 20 which is composed of the partial surfaces of thesurface region 2, which are not covered by the pattern regions 21 to 40,so that a planar reflecting surface is afforded there, from which themicrostructure shaped in the pattern regions 21 to 40 stands out.

It is however also possible for a transmissive element, a diffractiongrating, a hologram-producing diffraction structure or a matt structureto be shaped in the background region 20 instead of a planar reflectingelement.

If the diffraction structure of a hologram is shaped in the patternregions 21 to 39, then preferably a matt structure, a diffractiongrating or a diffraction structure of another hologram which differs inthe viewing direction and/or in respect of colour impression from thefirst hologram is shaped in the background region 20. If a mattstructure is shaped in the pattern regions 21 to 40, preferably a secondmatt structure with a different scattering characteristic is shaped inthe background region 20. If a diffraction grating is shaped in thepattern regions 21 to 40, preferably a matt structure or a diffractiongrating which differs from that diffraction grating in the gratingparameters, for example in the number of lines or orientation, is shapedin the background region 20.

For verification of the information encoded in the surface region 2(letter ‘V’), a verification element is used, comprising a line gratingor a printed line grating with a line spacing corresponding to that ofthe pattern regions 21 to 40. If the verification element is oriented onthe surface region 2 in such a way that it covers the pattern regions21, 22, 24, 26, 27, 29, 31, 32, 34, 36, 37 and 39, then the opticaleffect produced by the pattern regions 21 to 40 is only still producedin the partial region 3. Accordingly in that partial region 3 the viewerperceives an optical effect which arises out of the superimposition ofthe optical effect produced in the background region 20 and the opticaleffect produced in the pattern regions. In contrast, in the partialregion of the surface region 2, which surrounds the partial region 3,the viewer only still perceives the optical effect produced in thebackground region 20. If the verification element is oriented in such away that it covers the pattern regions 23, 25, 28, 30, 33, 35, 38 and40, the situation is reversed. If no verification element is applied tothe surface region 2, the human viewer, in the surface region, has anoptical impression which arises out of the superimposition of theoptical effect produced in the pattern regions and the optical effectproduced in the background region. If for example diffraction structuresof two holograms which differ in viewing direction and/or colourimpression are shaped in the pattern regions and in the backgroundregion, then, when viewing without a verification element, bothholograms can be seen by the viewer, while, when using a verificationelement, the one hologram is only visible in the partial region 3 andthe other hologram is only visible in the partial region of the surfaceregion 2, which surrounds the partial region 3.

As the average surface coverage of the meander-shaped substructuringdescribed by the substructuring function, in relation to the resolutioncapacity of the human eye, is constant, that does not influence theviewing impression which occurs in the above-described situations. Itcan however be discerned with a magnifying glass or a microscope and canserve as an additional security feature or for identification purposes.As already described above, additional optically perceptible effectswhich can serve as a further security feature occur due to thestructuring upon displacement of the verification element, in thesurface region 2.

A phase displacement of 180 degrees between the pattern regions of thepartial region 3 and the pattern regions surrounding same permits aparticularly high contrast when viewing through the verification elementas then the entire surface region of the pattern regions of the partialregion 3 can be covered whereas the pattern regions surrounding same arenot covered. It will be appreciated that in that respect it is alsopossible to deviate somewhat from the phase displacement of 180 degrees.In addition advantages can also be enjoyed by considerably deviatingfrom a phase displacement of 180 degrees in one partial region or theother and for example providing a phase displacement of 45 degrees or135 degrees. Thus it is possible for example to implement concealed greyscale images in which the grey scale is encoded by means of the phasedisplacement.

Instead of using a linear line grating for the arrangement of thepattern regions 21 to 40 it is possible to use a complex, for examplewave-shaped line grating, in which case also phase displacement of thepattern regions is implemented in partial regions of the line grating inorder to encode concealed items of information in the line grating. Averification element which covers surface regions in accordance withthat line grating is used for evaluation purposes.

Further possible options in regard to substructuring of pattern regionswill now be described with reference to FIGS. 3 a to FIG. 4.

FIG. 3 a shows a plurality of pattern regions 41 which are substructuredin accordance with a substructuring function describing a meander-shapedsubstructuring. In this case the substructuring function does not needto describe a continuous substructuring pattern. Thus FIG. 3 b showssubstructured pattern regions 42 which are substructured in accordancewith a substructuring pattern made up of a plurality of similar elements43.

The spacings of the individual elements or the orientation of theindividual elements can be varied in that case as long as the averagesurface coverage of the substructuring pattern, which can be resolved bythe human eye, remains constant.

Thus FIG. 3 c shows the substructuring of two adjacent pattern regions44 and 45 in which the spacings of the individual elements 43 arevaried. As shown in FIG. 3 c in that case the average surface coverageof the substructuring pattern remains constant. By virtue of such anarrangement of spacings, it is possible for additional, for exampleelectronically evaluatable items of information to be encoded in theoptical security element.

FIG. 3 d now shows the possibility of encoding items of information intothe substructuring not only by virtue of differing spacing but also byvirtue of differing orientation of individual elements, and in that casekeeping constant the average surface coverage of the substructuringpattern, which can be resolved by the human eye.

Thus FIG. 3 d shows three adjacent pattern regions 46, 47 and 48 whichare each formed by five individual elements which differ in respect oftheir orientation and their spacing.

Furthermore it is also possible for items of information to beadditionally encoded into the substructuring pattern by a differingphase position in respect of adjacent individual elements.

FIG. 4 now shows a surface region 5 which is divided into a backgroundregion 50 and pattern regions 51 to 90. In this case the pattern regions50 to 90 are substructured in accordance with a substructuring functionwhich writes a microtext or nanotext. The letter height of thatmicrotext or nanotext is 60 μm in the embodiment shown in FIG. 4.

The surface regions in a V-shaped partial region 6 of the surface region5 are phase-displaced in relation to the pattern regions surroundingthem, similarly to the embodiment shown in FIG. 2. The part of theoptical security element which forms the background region 50 is of aconfiguration like the background region 20 shown in FIGS. 1 and 2 andthus for example has a reflecting planar surface, a diffraction grating,a diffraction structure of a hologram or a matt structure. The regionsof the optical security element, which are covered by the substructuredpattern regions 51 to 90, are of a configuration like the patternregions 21 to 40 of FIG. 2 and FIG. 1 and for example have a diffractiongrating, a diffraction structure of a hologram or a matt structure.

It will be appreciated that, instead of the letter combination ‘TEXT’shown in FIG. 4 and used for the substructuring, it is also possible toselect a different kind of letter combination which can also reproduce acomplex content. Furthermore it is also possible to use nano-images forthe substructuring instead of or in combination with letters and lettercombinations.

It is further also possible for the substructuring to be composed of acombination of various substructuring options as described hereinbefore,or for the one substructuring or the other to be used for exampleline-wise alternately.

FIG. 5 a thus shows for example a substructuring of pattern regions andbackground region, in which the background region is structured with asubstructuring 94 and the pattern regions with a substructuring 93.

In this case, different optical-diffraction structures can be providedin the regions of the substructurings 93 and 94. The linear grating isagain displaced by half a period in accordance with the concealedinformation to be encoded. If a verification element (for example alinear grating comprising transparent and opaque regions involving thesame period) is applied, it covers for example the structures in thesubstructuring 94 on the left-hand side while the verifiercorrespondingly covers the structures in the substructuring 93 on theright-hand side.

In comparison with the variants described hereinbefore, this involves abackground region of the meander configuration, which is additionallysubstructured in accordance with ‘TEXT’.

In addition for example mirrors or a further structure which differsfrom the two optical-diffraction structures of the line gratings, forexample in the meander configuration or text, can be disposed in thebackground of two line gratings which are substructured in differentways.

FIG. 5 b shows a further possible option of substructuring of patternregions.

FIG. 5 b shows a plurality of substructured pattern regions 91 which arephase-displaced in relation to substructured pattern regions 92. Asshown in FIG. 5 the pattern regions 91 and 92 are substructured by meansof a respective asymmetrical substructuring pattern so that the centroidof the pattern region is displaced upwardly or downwardly respectivelyby the substructuring.

That effect can be used to displace in each case only the centroid ofthe substructured pattern region afforded by the substructuring, by halfa period of the verification element, instead of the phase displacementshown in FIG. 2 and FIG. 4, in the respective partial regions 3 and 6.As shown in FIG. 5 b in that way the phase displacement by half a periodcan be replaced by a mirroring.

It will be appreciated that it is also possible, instead of themirror-symmetrical substructuring patterns shown in FIG. 5 b, for thepattern regions 91 and 92, to use any different substructuring patternswhich differ in terms of their centroid. It is advantageous in thatrespect however if the average surface coverage of those substructuringpatterns, in relation to the resolution capacity of the human eye,remains constant and is identical so that the concealed informationcannot be seen by the naked eye.

FIGS. 6 a to 6 c show further possible options of the substructuring ofpattern regions by the superimposition of a two-dimensional grating.

Thus FIG. 6 a shows a surface region 110 with a plurality of patternregions 111 to 119 and FIG. 6 b shows a surface region 120 with aplurality of pattern regions 121 to 126. As shown therein thesubstructuring of the pattern regions is afforded in each case by thesuperimposition of dot and line gratings. It will be seen thatrespective adjacent pattern regions can have a different pattern whicharises out of that superimposition. In section however each patternregion is of the same optical density so that a surface which iscorrespondingly occupied with optical-diffraction structures appearshomogeneous in effect to a viewer as that substructuring cannot beresolved by the eye.

FIG. 6 c shows a surface region 130 with pattern regions 131 to 136 and137 to 144, which are arranged in accordance with a two-dimensionalgrating. The principle of substructuring by means of a superimposingline and dot grating, which is shown in FIGS. 6 a and 6 b, is used hereto encode two different concealed items of information in the patternregions, which can be evaluated at two different orientation directions(0 degree and 90 degrees) of the verification element.

FIG. 7 shows a plurality of partial regions 140, 150, 160, 170 and 180of a surface region. A plurality of substructured pattern regions 142and 141 which are phase-displaced relative to each other are arranged inthe partial region 140. A respective plurality of substructured patternregions 152 and 151, 162 and 161, 172 and 171, and 182 and 181respectively, which are phase-displaced relative to each other, arearranged in each of the pattern regions 150, 160, 170 and 180.

As can be seen from FIG. 7 the substructuring patterns differ in thepartial regions 140, 150, 160, 170 and 180 in such a way that theiraverage surface coverage which can be resolved by the human eye isdifferent. Accordingly the average surface coverage of thesubstructuring pattern is only constant in the respective partial regionso that the information encoded by the phase displacement remainsinvisible to the human viewer without the aid of a verification element.

Such substructuring of the pattern regions, which is in part different,provides that the ratio of the average surface coverage by patternregions and by the background region is partially varied so that in parteither the optical effect produced in the pattern regions is more in theforeground or the optical effect produced in the background region ismore in the foreground. In that case the concealed information can beseen by means of the verification element at a very high level ofcontrast with an average surface ratio of pattern regions to backgroundregion. The contrast disappears at 0% or 100% surface coverage by thepattern regions.

Thus such a partial variation in the substructuring function which canalso occur ‘quasi-continuously’ can provide for generating a furthersecurity feature which is perceptible for the viewer, for example imageinformation in a grey scale representation.

1. An optical security element having a substrate layer, wherein a firstmicrostructure for producing a first optically perceptible effect isshaped region-wise into the substrate layer in a surface region of thesubstrate layer, wherein the first microstructure is a diffractionstructure, in particular a diffraction grating, a diffraction structurefor producing a hologram or a matt structure, that the surface region isdivided into microscopically fine pattern regions and a backgroundregion and the first microstructure is shaped in the pattern regions butnot in the background region, that the microscopically fine patternregions in the surface region are arranged in the form of a moirepattern into which a concealed item of information which can beevaluated by means of an associated verification element is encoded as asecurity feature, wherein the moire pattern has at least one linegrating with a plurality of lines at a line spacing in the range of 40to 200 μm and the line grating is phase-displaced in region-wise mannerto produce the concealed information, and that the microscopically finepattern regions are further substructured in accordance with asubstructuring function which describes a microscopic substructuring,which serves as a further security feature, of the moiré pattern andwhich encodes additional items of information in the surface region. 2.An optical security element according to claim 1, wherein the firstmicrostructure is a first diffraction grating.
 3. An optical securityelement according to claim 1, wherein the first microstructure is adiffraction structure for producing a first hologram.
 4. An opticalsecurity element according to claim 1, wherein the first microstructureis a first matt structure.
 5. An optical security element according toclaim 1, wherein a reflecting surface is arranged in the backgroundregion.
 6. An optical security element according to claim 1, wherein asecond microstructure is shaped in the background region, thatmicrostructure being formed by a second diffraction grating which isdifferent from the first diffraction grating.
 7. An optical securityelement according to claim 1, wherein a second microstructure is shapedin the background region, said second microstructure being formed by adiffraction structure for producing a second hologram.
 8. An opticalsecurity element according to claim 1, wherein a second microstructureis shaped in the background region, said second microstructure beingformed by a second matt structure which is different from the first mattstructure.
 9. An optical security element according to claim 1, whereinthe line grating has regions in which the lines of the line grating arecurved.
 10. An optical security element according to claim 1, whereinthe moire pattern comprises two line gratings which are rotated relativeto each other through at least 45 degrees.
 11. An optical securityelement according to claim 1, wherein the moire pattern comprises atwo-dimensional grating.
 12. An optical security element according toclaim 1, wherein the average surface coverage of the moire pattern inrelation to the resolution capacity of the human eye is constant.
 13. Anoptical security element according to claim 1, wherein the averagesurface coverage of the substructuring described by the substructuringfunction in relation to the resolution capacity of the human eye isconstant.
 14. An optical security element according to claim 1, whereinthe average surface coverage of the moire pattern is varied by partiallydifferent substructuring.
 15. An optical security element according toclaim 1, wherein the substructuring function describes a continuoussubstructuring pattern.
 16. An optical security element according toclaim 1, wherein the substructuring function describes a non-continuoussubstructuring pattern.
 17. An optical security element according toclaim 15, wherein the substructuring function describes a substructuringpattern made up of a plurality of similar individual elements.
 18. Anoptical security element according to claim 17, wherein the spacings ofthe individual elements and/or their orientation is varied for encodingof a further item of information but the average surface coverage of thesubstructuring pattern, which can be resolved by the human eye, remainsconstant.
 19. An optical security element according to claim 1, whereinthe substructuring function describes a microtext or nanotext which ispreferably of a letter height in the range of 20 to 100 μm.
 20. Anoptical security element according to claim 1, wherein a two-dimensionalgrating is superimposed on the substructuring function.
 21. An opticalsecurity element according to claim 1, wherein the pattern regions aresubstructured with an asymmetrical surface profile and that thecentroids of the pattern regions are phase-displaced in region-wisemanner to produce the concealed information.